A test of the predictive power of four physiological variables which change with age showed that poor performance on creatinine clearance, forced expiratory volume, and systolic blood pressure was associated with mortality. Poor glucose tolerance, however, did not predict mortality and, therefore, may not be of great significance. Glycosylated hemoglobin levels may be a better test of the hypothesis that relative hyperglycemia is harmful even in those not overtly diabetic; several new sources of variance for this variable have been found and this should add to the reproducibility and reliability of the assay. Basal levels of growth hormone and of glucagon do not change with age in our subjects and, therefore, do not contribute to decline in glucose tolerance with age.